Disclaimer: The contents of this guidance document does not have the force and effect of law and is not meant to bind the public in any way. This document is intended only to provide clarity to the public regarding existing requirements under the law or agency policies. UNITED STATES DEPARTMENT OF AGRICULTURE RURAL UTILITIES SERVICE BULLETIN 1724D-114 RD-GD-2017-90 SUBJECT: Voltage Regulator Application on Rural Distribution Systems TO: RUS Electric Borrowers and RUS Electric Staff EFFECTIVE DATE: Date of Approval. OFFICE OF PRIMARY INTEREST: Electric Staff Division. INSTRUCTIONS: This is a new bulletin. AVAILABILITY: This bulletin is available on the Rural Utilities Service (RUS) website at: www.rd.usda.gov/publications/regulations-guidelines/bulletins/electric. PURPOSE: This bulletin provides fundamental information about voltage regulators, their controls, and their application on rural distribution systems for Rural Utilities Service (RUS) borrowers and others. December 4, 2017 Date Bulletin 1724D-114 Page 2 1 INTRODUCTION ...................................................................................................................4 2 VOLTAGE STANDARDS ......................................................................................................4 3 VOLTAGE REGULATION ON DISTRIBUTION SYSTEMS .............................................6 4 VOLTAGE REGULATORS ...................................................................................................9 5 SUBSTATION VOLTAGE REGULATORS AND SYSTEM VOLTAGE LEVELS .........26 6 LINE VOLTAGE REGULATOR APPLICATION ..............................................................32 7 VOLTAGE REGULATOR INSTALLATION .....................................................................35 8 VOLTAGE REGULATOR AND CAPACITOR APPLICATIONS .....................................36 9 VOLTAGE REGULATOR PROTECTION..........................................................................42 10 REFERENCES ......................................................................................................................43 Exhibits Exhibit A – Derivation of Formulas for Calculating Voltage Drop and Voltage Regulation Exhibit B – Effect of Shunt Capacitor on Source Current and Line Voltage INDEX: Regulators (Voltage) Voltage Regulators Voltages (Distribution System) ABBREVIATIONS AC Alternating Current LDC Line Drop Compensator ANSI American National Standards LTC Load Tap Changer Institute PT Potential Transformer CFR Code of Federal Regulations R Resistance CT Current Transformer RLC Resistor-Inductor-Capacitor EEPROM Electrically Erasable and rms Root Mean Square Programmable Read-Only RUS Rural Utilities Service Memory SCADA Supervisory Control and Data IEEE Institute of Electrical and Acquisition Electronics Engineers VD Voltage Drop kV Kilovolt VR Voltage Regulation kVA Kilovolt-Ampere VSC Voltage Sensing Circuit kvar Kilovolt-Ampere Reactive X Reactance DEFINITIONS Bandwidth — The difference between the maximum and minimum allowable voltages within which a voltage regulator will hold the output voltage. Bulletin 1724D-114 Page 3 Base Voltage — Base voltage is a reference voltage value which is a common denominator to the nominal voltage ratings of transmission and distribution lines, transmission and distribution equipment, and utilization equipment. For example, the base voltage of a transmission line having a nominal voltage rating of 34,500 volts is 115 volts; the base voltage of a distribution line having a nominal voltage rating of 7,200 volts is 120 volts. In general, distribution lines and associated equipment having a nominal rating from 2,400 volts through 19,920 volts will have a 120-volt base, and the nominal voltage rating of utilization equipment served by these voltages will also have a 120-volt base. Maximum Voltage — Maximum voltage is the greatest sustained five-minute mean or average voltage. Minimum Voltage — Minimum voltage is the smallest sustained five-minute mean or average voltage. Nominal Voltage — The nominal voltage of a circuit or system is a nominal value assigned to the circuit or system for the purpose of conveniently designating its voltage class. For example, the nominal rural residential voltage is 120 volts, although the voltage may actually range from 114 volts to 126 volts. Rated Voltage — Rated voltage is the voltage at which performance and operating characteristics of utilization equipment are referred. Service Voltage — Service voltage is the voltage at the point where the electric systems of the supplier and the user are connected. In rural electric systems, this is usually considered the voltage at the meter socket or service entrance switch. Utilization Equipment — Utilization equipment refers to consumer electrical loads, such as electrical appliances, lighting fixtures, heaters, and motors. Utilization Voltage — Utilization voltage is the voltage at the line terminals of utilization equipment. This is generally considered to be the voltage at the terminals of the device or appliance or the voltage at the convenience outlet to which these terminals are connected. Voltage Drop — Voltage drop (in a supply system) is the difference between the voltages at the transmitting and receiving ends of a circuit, main, or service. Voltage Regulation — Voltage regulation of a line is the percent voltage drop with respect to the receiving-end voltage. Voltage Spread — Voltage spread is the difference between maximum and minimum voltage at a particular location in the distribution system. Bulletin 1724D-114 Page 4 1 INTRODUCTION Providing acceptable voltage levels to consumers is vital to the proper operation of utilization equipment (i.e., electrical appliances, equipment, and other electrical loads). If utilization equipment is operated outside its prescribed voltage limits, equipment damage and erratic performance could result. An overvoltage condition, for example, can significantly shorten equipment life, decrease power factors of motors, and burn out lights and heating elements. On the other hand, an undervoltage condition can result in overheating of motors, dim lights, and cause other potential equipment damage. Hence, it is important for electric utilities to regulate their distribution system voltage for proper operation of electrical equipment. It is impractical for electric utilities to provide each consumer with constant voltage that exactly matches the rated voltage of utilization equipment. Thus, the standard practice for utilities is to provide consumers with voltage levels that are within voltage ranges established by the American National Standards Institute (ANSI) and the Rural Utilities Service (RUS). To ensure that utilization voltage is kept within prescribed limits, electric utilities use voltage regulators on their distribution systems as a standard practice. This bulletin provides fundamental information about voltage regulators, their controls, and their application on rural distribution systems for RUS borrowers and others. 2 VOLTAGE STANDARDS In many states, the limits of voltage spread permitted at consumers’ meters are established by the state regulatory commissions. In states where borrowers are not subject to such controls, RUS recommends the limits established by the American National Standards Institute in ANSI C84.1-2016, “Electric Power Systems and Equipment—Voltage Ratings (60 Hertz).” a Nominal System Voltage Standards Table 1 presents the nominal voltages for secondary circuits established in ANSI C84.1-2016 and is recommended by RUS for its borrowers to serve their residential and commercial consumers. The voltage limits established and recommended in ANSI C84.1-2016 are used by the majority of the electric utilities in the United States. TABLE 1: Nominal Low-Voltage Standards.1 Nominal System Voltages Connection and Phase 120-V Two-wire, single-phase 120/240-V Three-wire, single-phase 240/120-V Four-wire, three-phase delta 208Y/120-V Four-wire, three-phase wye 480Y/277-V Four-wire, three-phase wye 480-V Three-wire, three-phase delta Bulletin 1724D-114 Page 5 b ANSI Recommended Voltage Limits ANSI Standard C84.1-2016 establishes voltage limits. The maximum and minimum utilization voltage limits for 120- to 480-volt circuits are shown in Table 2. TABLE 2: ANSI Recommended Service and Utilization Voltage Ranges.1 Nominal Minimum Maximum System Utilization Service Utilization and Voltage Voltage Voltage Service Voltage Range (Volts) (Volts) (Volts) (Volts) A 120 108 114 126 A 120/240 108/216 114/228 126/252 A 240/120 216/108 228/114 252/126 A 208Y/120 187Y/108 197Y/114 218Y/126 A 480Y/277 432Y/249 456Y/263 504Y/291 A 480 432 456 504 B 120 104 110 127 B 120/240 104/208 110/220 127/254 B 240/120 208/104 220/110 254/127 B 208Y/120 180Y/104 191Y/110 220Y/127 B 480Y/277 416Y/240 440Y/254 508Y/293 B 480 416 440 508 As shown in Table 2, for any given nominal system voltage, the actual operating values can vary over various ranges of voltage limits. ANSI C84.1-2016 categorizes voltage ranges into Range A and Range B. Range A is bounded by voltage limits within which service voltages have to be held. Range A includes the majority of the existing utilization equipment operating voltages that produce satisfactory operation of consumer equipment. Range B is bounded by voltage limits that are slightly above and below the Range A voltage limits. In this range, consumer equipment may still operate satisfactorily, although its performance may be less than warranted by the manufacturer. Range B voltage limits can be tolerated